1. Field of the Invention
The present invention relates to a semiconductor device which has a circuit including a thin film transistor (hereinafter also referred to as a TFT) in which a channel formation region is formed using an oxide semiconductor film and a method for manufacturing the semiconductor device. For example, the present invention relates to an electronic device having an electro-optical device typified by a liquid crystal display panel or a light-emitting display device including an organic light-emitting element.
It is to be noted that the semiconductor device in this specification refers to all devices that can function by utilizing semiconductor characteristics, and electro-optical devices, semiconductor circuits, and electronic devices are all semiconductor devices.
2. Description of the Related Art
Various metal oxides are used for a variety of applications. Indium oxide is a well-known material and is used as a light-transmitting electrode material which is needed for a liquid crystal display or the like.
Some metal oxides have semiconductor characteristics. Examples of metal oxides having semiconductor characteristics include tungsten oxide, tin oxide, indium oxide, zinc oxide, and the like. Thin film transistors in which a channel formation region is formed using such metal oxides having semiconductor characteristics have already been disclosed (Patent Documents 1 to 4, Non-Patent Document 1).
Further, not only single oxides but also multiple oxides are known as metal oxides. For example, InGaO3(ZnO)m (m is a natural number) which is a homologous compound is known as a multiple oxide semiconductor including In, Ga, and Zn (Non-Patent Documents 2 to 4).
In addition, it has been confirmed that an oxide semiconductor including such an In—Ga—Zn-based oxide can be used as a channel layer of a thin film transistor (Patent Document 5, and Non-Patent Documents 5 and 6).